Hach pHD Manual Básico Del Usuario página 19

6.4 Prepare for storage
For short-term storage (when the sensor is out of the process for more than one hour), fill the
protective cap with pH 4 buffer or distilled water and put the cap back on the sensor. Keep the
process electrode and reference junction salt bridge moist to avoid slow response when the sensor is
returned to operation.
For extended storage, repeat the short-term storage procedure every 2 to 4 weeks, depending on the
environmental conditions. Refer to
Section 7 Troubleshooting
7.1 Intermittent data
During calibration, data is not sent to the datalog. Thus, the datalog can have areas where the data is
intermittent.
7.2 Test the pH sensor
Pre-requisites: Two pH buffers and a multimeter.
If a calibration fails, first complete the maintenance procedures in
1. Put the sensor in a pH 7 buffer solution and wait for the temperature of the sensor and buffer to
reach room temperature.
2. Disconnect the red, green, yellow and black sensor wires from the module or digital gateway.
3. Measure the resistance between the yellow and black wires to verify the operation of the
temperature element. The resistance should be between 250 and 350 ohms at approximately
25 ºC.
If the temperature element is good, reconnect the yellow and black wires to the module.
4. Measure the DC mV with the multimeter (+) lead connected to the red wire and the (–) lead
connected to the green wire. The reading should be between –50 and + 50 mV.
If the reading is outside of these limits, clean the sensor and change the salt bridge and standard
cell solution.
5. With the multimeter still connected the same way, rinse the sensor with water and put it in a pH
4 or pH 10 buffer solution. Wait for the temperature of the sensor and buffer to reach room
temperature.
6. Compare the mV reading in the pH 4 or 10 buffer to the reading in the pH 7 buffer. The reading
should differ by approximately 160 mV.
If the difference is less than 160 mV, call technical support.
7.3 Test the ORP sensor
Pre-requisites: 200 mV ORP reference solution, multimeter.
If a calibration fails, first complete the maintenance procedures in
1. Put the sensor in a 200 mV reference solution and wait for the temperature of the sensor and
solution to reach room temperature.
2. Disconnect the red, green, yellow and black sensor wires from the module or digital gateway.
3. Measure the resistance between the yellow and black wires to verify the operation of the
temperature element. The resistance should be between 250 and 350 ohms at approximately
25 ºC.
If the temperature element is good, reconnect the yellow and black wires to the module.
4. Measure the DC mV with the multimeter (+) lead connected to the red wire and the (–) lead
connected to the green wire. The reading should be between 160 and 240 mV.
If the reading is outside of these limits, call technical support.
Specifications on page 3 for temperature storage limits.
Maintenance on page 15.
Maintenance on page 15.
English 19